Method and apparatus for chromatography-high field asymmetric waveform ion mobility spectrometry

ABSTRACT

Method and apparatus for chromatographic high field asymmetric waveform ion mobility spectrometry, including a gas chromatographic analyzer section intimately coupled with an ionization section, an ion filter section, and an ion detection section, in which the sample compounds are at least somewhat separated prior to ionization, and ion filtering proceeds in a planar chamber under influence of high field asymmetric periodic signals, with detection integrated into the flow path, for producing accurate, real-time, orthogonal data for identification of a broad range of chemical compounds.

This application is a continuation-in-part of Application Ser. No.09/358,312 filed Jul. 21, 1999 now U.S. Pat. No. 6,495,823.

BACKGROUND OF THE INVENTION

The present invention relates to spectrometry, and more particularly, tomethodology and apparatus for the analysis of compounds bychromatography-high field asymmetric waveform ion mobility spectrometry.

There is a developing interest in making in situ measurements ofchemicals present in complex mixtures at industrial or environmentalvenues. A fully functional chemical sensor system may incorporate afront end, e.g., a gas chromatography (GC) analyzer as a compoundseparator, and then a detector, i.e., a spectrometer.

Gas chromatography is a chemical compound separation method in which adiscrete gas sample (composed of a mixture of chemical components) isintroduced via a shutter arrangement into a GC column. Components of theintroduced gas sample are partitioned between two phases: one phase is astationary bed with a large surface area, and the other is a gas whichpercolates through the stationary bed. The sample is vaporized andcarried by the mobile gas phase (the carrier gas) through the column.Samples partition (equilibrate) into the stationary (liquid) phase,based on their solubilities into the column coating at the giventemperature. The components of the sample separate from one anotherbased on their relative vapor pressures and affinities for thestationary bed, this process is called elution.

The heart of the chromatograph is the column; the first ones were metaltubes packed with inert supports on which stationary liquids werecoated. Presently, the most popular columns are made of fused silica andare open tubes with capillary dimensions. The stationary liquid phase iscoated on the inside surface of the capillary wall.

Compounds are discriminated by the time that they are retained in the GCcolumn (the time from sample injection to the time the peak maximumappears). Chemical species are identified from a sample based on theirretention time. The height of any one of these peaks indicates theintensity or concentration of the specific detected compound.

A carrier gas (e.g., helium, filtered air, nitrogen) flows continuouslythrough the injection port, and the column. The flow rate of the carriergas must be carefully controlled to ensure reproducible retention timesand to minimize detector drift and noise. The sample is usually injected(often with a microsyringe) into a heated injection port where it isvaporized and carried into the column, often capillary columns 15 to 30meters long are used but for fast GC they can be significantly shorter(less than 1 meter), coated on the inside with a thin (e.g., 0.2 micron)film of high boiling liquid (the stationary phase). The samplepartitions between the mobile and stationary phases, and is separatedinto individual components based on relative solubility in the liquidphase and relative vapor pressures. After the column, the carrier gasand sample pass through a detector that typically measures the quantityof the sample, and produces an electrical signal representative thereof.

Certain components of high speed or portable GC analyzers have reachedadvanced stages of refinement. These include improved columns andinjectors, and heaters that achieve precise temperature control of thecolumn. Even so, detectors for portable gas chromatographs still sufferfrom relatively poor detection limits and sensitivity. In addition, GCanalyzers combined with any of the conventional detectors—flameionization detectors (FID), thermal conductivity detectors, orphoto-ionization detectors—simply produce a signal indicating thepresence of a compound eluted from the GC column. However, presenceindication alone is often inadequate, and it is often desirable toobtain additional specific information that can enable unambiguouscompound identification.

One approach to unambiguous compound identification employs acombination of instruments capable of providing an orthogonal set ofinformation for each chromatographic peak. (The term orthogonal will beappreciated by those skilled in the art to mean data which enablesmultiple levels of reliable and accurate identification of a particularspecies, and uses a different property of the compound foridentification.) One such combination of instruments is a GC attached toa mass spectrometer (MS). The mass spectrometer is generally consideredone of the most definitive detectors for compound identification, as itgenerates a fingerprint pattern of fragment ions for each compoundeluting from the GC. Use of the mass spectrometer as the detectordramatically increases the value of analytical separation provided bythe GC. The combined GC-MS information, in most cases, is sufficient forunambiguous identification of the compound.

Unfortunately, the GC-MS is not well suited for small, low cost,fieldable instruments. Therefore there is still a strong need to be metwith a fieldable chemical sensor that can generate reliable orthogonalinformation. A successful field instrument should include both a smallinjector/column and a small detector/spectrometer and yet be able torapidly produce unambiguous orthogonal data for identification of adetected compound.

While GC's are continuously being miniaturized and reduced in cost, massspectrometers are still very expensive, easily exceeding $100K. Theirsize remains relatively large, making them difficult to deploy in thefield. Mass spectrometers also suffer from the need to operate at lowpressures, and their spectra can be difficult to interpret oftenrequiring a highly trained operator. The search therefore has continuedfor fieldable spectrometer.

Time-of-flight Ion Mobility Spectrometers (TOF-IMS) have been describedas detectors for gas chromatographs from early in the development of ionmobility spectrometry and the first successful use of TOF-IMS detectorswith capillary chromatography occurred in 1982. High-speed response andlow memory effects were attained and the gas phase ion chemistry insidethe TOF-IMS can be highly reproducible providing the foundation to gleanchemical class information from mobility spectra. Thus, TOF-IMS, asionization detectors for GC, do exhibit functional parallels to massspectrometers, except all processes in IMS occur at ambient pressuremaking vacuum systems unnecessary. The IMS spectra is also simpler tointerpret since it contains fewer peaks, due to less ion fragmentation.The usefulness of a gas chromatograph with TOF-IMS detector has beenrecognized for air quality monitoring, chemical agent monitoring,explosives detection, and for some environmental uses.

Fieldability still remains a problem for TOF-IMS. Despite advances overthe past decade, TOF-IMS drift tubes are still comparatively large andexpensive and suffer from losses in detection limits when made small.The search therefore still continues for a successful field instrumentthat includes both a small ion injector/column and a smalldetector/spectrometer and yet is able to rapidly produce unambiguousorthogonal data for identification of a detected compound.

The high field asymmetric waveform ion mobility spectrometer (FAIMS) isan alternative to the TOF-IMS. In a FAIMS device, a gas sample thatcontains a chemical compound is subjected to an ionization source. Ionsfrom the ionized gas sample are drawn into an ion filter and subjectedto a high field asymmetric waveform ion mobility filtering technique.Select ion species allowed through the filter are then passed to an iondetector, enabling indication of a selected species.

The FAIMS filtering technique involves passing ions in a carrier gasthrough strong electric fields between the filter electrodes. The fieldsare created by application of an asymmetric period voltage (typicallyalong with a further control bias) to the filter electrodes.

The process achieves a filtering effect by accentuating differences inion mobility. The asymmetric field alternates between a high and lowfield strength condition that causes the ions to move in response to thefield according to their mobility. Typically the mobility in the highfield differs from that of the low field. That mobility differenceproduces a net displacement of the ions as they travel in the gas flowthrough the filter. In absence of a compensating bias signal, the ionswill hit one of the filter electrodes and will be neutralized. In thepresence of a specific bias signal, a particular ion species will bereturned toward the center of the flow path and will pass through thefilter. The amount of change in mobility in response to the asymmetricfield is compound-dependent. This permits separation of ions from eachother according to their species, in the presence of an appropriatelyset bias.

In the past, Mine Safety Appliances Co. (MSA) made an attempt at afunctional FAIMS implementation in a cylindrical device, such asdisclosed in U.S. Pat. No. 5,420,424. (It is referred to by MSA as aField Ion Spectrometer (FIS), see FIG. 1.) The device is complex, withmany parts, and is somewhat limited in utility.

Fast detection is a sought-after feature of a Wieldable detectiondevice. One characteristic of known FAIMS devices is the relatively slowdetection time. However, the GC operates much more rapidly, such thatthe known FAIMS devices cannot generate a complete spectra of the ionspresent under each GC peak. Therefore these FAIMS devices would have tobe limited to a single compound detection mode if coupled to a GC, witha response time of about 10 seconds. Any additional compound that isdesired to be measured will take approximately an additional 10 secondsto measure.

While the foregoing arrangements are adequate for a number ofapplications, it is still desirable to have a small, fieldable iondetector/spectrometer that can render real-time or near real-timeindications of detected chemical compounds, such as for use on abattlefield and in other environments.

Furthermore, a GC-FAIMS arrangement, focused as it is on one species ata time, is incapable of simultaneous detection of a broad range ofspecies, such as would be useful for airport security detectors, or on abattlefield, or in industrial environments. Such equipment is alsoincapable of simultaneous detection of both positive and negative ionsin a gas sample.

It is therefore an object of the present invention to provide afunctional, small, fieldable ion detector/spectrometer that overcomesthe limitations of the prior art.

It is a further object of the present invention to provide a chemicalsensor that features the benefits of GC and FAIMS but is able to operaterapidly with reduced processing time.

It is a further object of the present invention to provide a chemicalsensor that features the benefits of GC and FAIMS but is able to detectmultiple species at one time.

It is a further object of the present invention to provide a chemicalsensor that features the benefits of GC and FAIMS but is able togenerate orthogonal data that fully identifies a detected species.

It is a further object of the present invention to provide a chemicalsensor that features the benefits of GC and FAIMS but is able to detectpositive and negative ions simultaneously.

It is a further object of the present invention to provide a fieldablechemical sensor that includes both a small ion injector/column and asmall detector/spectrometer and yet is able to rapidly produceunambiguous orthogonal data for identification of a variety of chemicalcompounds in a sample.

It is a further object of the present invention to enable a new class ofchemical sensors that can rapidly produce unambiguous, real-time or nearreal-time, in-situ, orthogonal data for identification of a wide rangeof chemical compounds.

It is a further object of the present invention to provide sensors thathave the ability to detect both positive and negative ionssimultaneously and achieving reduction of analysis time.

It is a further object of the present invention to provide a class ofsensors that have the ability to use the reactant ion peak to extractthe retention time data from a GC sample.

It is a further object of the present invention to provide a class ofsensors that have the ability to make 2-D and 3-D displays of speciesinformation as obtained.

It is a further object of the present invention to provide a class ofsensors that enable use of pattern recognition algorithms to extractspecies information. It is a further object of the present invention toprovide a class of sensors that do not require consumables forionization.

It is a further object of the present invention to provide a class ofsensors that provide differential-mobility spectra information inaddition to the retention time data.

It is a further object of the present invention to provide a class ofsensors that can eliminate the need to run standards through the GC.

It is a further object of the present invention to provide a class ofsensors utilizing arrays of FAIMS devices each tuned to detect aparticular compound, such that multiple compounds can be simultaneouslydetected rapidly, with simplified electronics.

It is a further object of the present invention to provide a GC detectorwhich detects compounds by ionizing eluted sample and uses differentamplitudes of an applied high filed asymmetric waveform to producedifferent levels of ion clusters, which can be useful in more precisespecies identification.

It is a further object of the present invention to provide a class ofsensors utilizing arrays of FAIMS devices to provide redundancy in iondetected.

It is a further object of the present invention to provide a class ofsensors utilizing arrays of FAIMS devices where each ion filter has itsown flow path (or flow channel) and is doped with a different dopant forbetter compound identification.

It is a further object of the present invention to provide a class ofsensors utilizing arrays of FAIMS devices each swept over an assignedbias range of the spectrum to obtain faster analysis of the contents ofan eluted GC peak.

It is a further object of the present invention to provide a class ofdetectors that can provide information on the cluster state of ions andion kinetics by varying the amplitude of the high voltage asymmetricelectric field or by adjusting the flow rate of ions through the device.

It is a further object of the present invention to provide a chemicalsensor that features the benefits of GC and FAIMS but is able to detectpositive and negative ions simultaneously by providing a longitudinalflow path in which positive and negative ions are carried simultaneouslythrough the filter to the detector for simultaneous independentdetection.

It is a further object of the present invention to provide a class ofsensors that can detect samples over a wide range of concentrationsthrough a controlled dilution of the amount of sample delivered to thePFAIMS through appropriate control of the ratios the amounts of drift,carrier and sample gasses.

It is further an object of this invention to provide a class of sensorsthat can quantitatively detect samples over a wide range ofconcentrations through controlled dilution by regulating the amount ofions injected into the ion filter region by controlling the potentialson deflector electrodes.

SUMMARY OF THE INVENTION

These and other objects are well met by the presently disclosedinvention. The present invention overcomes cost, size or performancelimitations of MS, TOF-IMS, FAIMS, FIS and other prior art devices, in anovel method and apparatus for chemical species discrimination based ondifferences in ion mobility in a compact, fieldable package.

In one aspect of the invention, a portable chemical sensor is provided.In another aspect of the invention, improvements in laboratory equipmentfor substance identification are provided. In a preferred embodiment ofthe invention, a novel planar, high field asymmetric ion mobilityspectrometer (PFAIMS) device is coupled with a GC to achieve a new classof chemical sensor, i.e., the GC-PFAIMS chemical sensor.

Embodiments of the present invention enable fieldable chemical sensorsthat are able to rapidly produce accurate, real-time or near real-time,in-situ, orthogonal data for identification of a wide range of chemicalcompounds. In one aspect of the invention, a system is provided forgenerating multiple data for characterizing a chemical species in a gassample. Sensor systems according to the invention have the capability torender simultaneous detection of a broad range of species, and have thecapability of simultaneous detection of both positive and negative ionsin a gas sample. With high ionization energy sources, devices inpractice of the invention have the ability to use the reactant ion peakto extract retention time data from the GC. They have the ability togenerate differential-mobility spectra information in addition to theretention time data and can enable 2-D and 3-D display of speciesinformation, and it is even possible to use pattern recognitionalgorithms to extract species and additional information from theGC-PFAIMS detection data.

Still further surprising is that this can be achieved in acost-effective, compact, volume-manufacturable package that can operatein the field with low power requirements and yet it is able to generateorthogonal data that can fully identify various detected species.

In practice of the invention, the GC-PFAIMS offers high sensitivity(ppb-ppt) at low cost. These devices can also have the advantage of notrequiring any consumables for ionization (like hydrogen gas in a FID).Furthermore, in the field a GC with a flame ionization detector orthermal conductivity sensor must be calibrated using chemical standards,since retention times can shift due to changing environmental conditions(e.g., humidity, moisture etc.). However, in operation of the GC-PFAIMSof the present invention, a different detection principle than that ofthe GC itself is used, and therefore a second degree of information isprovided (i.e., providing differential mobility spectra for each peak ofthe GC), and this can be used to confirm the experimental results. Assuch the invention may be used to eliminate the complicated,time-consuming, need to run standards through the GC.

An embodiment of the present invention includes an inlet section, anionization section, an ion filtering section, an output section for ionspecies detection, a control section, and a section for gaschromatographic (GC) analysis of a gas sample, the GC section coupled tothe inlet section. The ionization section is disposed for ionizing a gassample from the GC section, the ionized sample passing to an ion filterin the ion filter section. The control section applies a high fieldasymmetric waveform voltage and a control function to the ion filteringsection to control species in the sample that are passed by the ionfilter to the output section for detection.

In an embodiment of the invention the ion filter section has at leastone substrate and the ion filter includes at least one planar electrodeon the substrate, wherein the electrode is isolated from the outputsection by the substrate.

In an embodiment of the invention, the ion filter section includes apair of insulated substrates and the ion filter includes at pair ofplanar electrodes, one on each a substrate.

In an embodiment of the invention, a planar housing defines a flow pathbetween the inlet section and the output section, the housing formedwith at least a pair of substrates that extend along the flow path. Theion filter is disposed in the flow path, and the filter includes atleast one pair of filter electrodes. At least one electrode is on eachsubstrate across from each other on the flow path. The control sectionis configured to apply an asymmetric periodic voltage to the ion filterelectrodes for controlling the travel of ions through the filter.

In yet another embodiment of the invention, a planar chamber defines aflow path, wherein the GC section separates the gas sample prior toionization, and filtering proceeds in the planar chamber under influenceof the high field asymmetric periodic signals, with detection integratedinto the flow path, for producing accurate, real-time, orthogonal datafor identification of a chemical species in the sample.

In another embodiment of the invention, the GC further includes acapillary column for delivering the gas sample into the inlet, the gassample includes a compound-containing carrier gas at a first flow rate.Preferably the inlet section, ionization section, ion filtering section,and output section communicate via a flow path, further including adrift gas source, the drift gas source supplying a drift gas into theinlet to carry the compound-containing carrier gas along the flow pathto the output section. One practice further includes a drift gas tube,wherein the capillary column is housed within the drift gas tube, thecapillary column having a column outlet delivering the carrier gas andthe drift gas flow surrounding the carrier gas flow at the columnoutlet. One practice including a coupling enabling receipt of the driftgas tube at the inlet with the capillary tube emptying into the inletsection from within the drift gas tube.

In another embodiment, the inlet section, ionization section, ionfiltering section, and output section are formed on a planar surface,the planar surface defining a flow path along a longitudinal axis forthe flow of ions in a gas sample from the ionization section, throughthe filter section, to the output section, wherein the output sectionincludes a detector for the detection of multiple ion speciessimultaneously. Preferably the detector includes a plurality ofelectrodes for detection of positive and negative ion speciessimultaneously.

In yet another embodiment of the invention, an ionizer is provided forionizing the sample and for creating reactant ions, the reactant ionsreacting with the ionized sample to create reactant ion data peaks,wherein the control section further includes a circuit for extraction ofretention time data from the sample by evaluation of the reactant iondata peaks.

In yet another embodiment, apparatus is provided for generation ofcomplementary data for evaluation of a chemical compound in the sample,that data including retention time and another variable. Preferably theanother variable is intensity of the detected ion species.

In practice of an embodiment of the invention, a display is coupled tothe output section for display of at least two dimensional datarepresentative of detected species. Preferably the control sectionfurther includes pattern recognition part for identification of an ionspecies according to data detected at the output section. The dataincludes differential mobility spectra and retention time data in apreferred embodiment.

In yet another embodiment, an isolation part joins the ion filteringsection and output section, ions being delivered to the ion filter fromthe ionization section via a flow path, the isolation part facilitatingnon-conductive connection of the ion filter and the output section.

In yet another embodiment, the ion filtering section is furthercharacterized by providing a short drift tube for rapid travel offiltered ions to the output part for detection. Preferably the ionfilter further includes a pair of electrodes, the electrodes facing eachother across the flow drift tube, wherein the ion filter further mayinclude a pair of electrodes, wherein the control section applies thehigh field asymmetric period voltage and control function as a controlfield to pair of electrodes to control species in the sample that arepassed by the ion filter to the output section for detection, the drifttube defining a first flow path region for application of the controlfield to ions in the ion filter, the ion filter being located in thefirst flow path region. The output section further includes an iondetector region, the drift tube defining a second flow path region, theisolation part being located in the second flow path region after thefirst region and before the detector region, and the ion filter partpasses ions in the drift tube under influence of the control field. Ionsthat are passed by the filter part travel through the isolation part tothe detector region for detection, the isolation part isolating thecontrol field from the detector region. Alternatively, further includinga pair of substrates, the substrates defining the drift tube, whereinthe electrodes are electrically insulated and the substrates areelectrically insulating, wherein the substrates may be planar.

In a further embodiment, at least a pair of substrates defines betweenthem a flow path for the flow of ions, with a plurality of electrodes,including a pair of ion filter electrodes, disposed in the flow pathbetween the inlet section and output section, one filter electrodeassociated with each substrate, the ion filter configured for receivingsamples included of a variety of ion species and the filter electrodescooperating with the control section applying to control the ions, theion filter simultaneously passing a selected plurality of ion species tothe detector part from the sample. Preferably, the output part furtherincludes a detector part, the detector part enabling simultaneousdetection of the selected plurality of ion species passed by the filter.The control section may provide separate independent outputs at thedetector part, the outputs providing signals representative of speciesdetected simultaneously from within the samples. The detector part maybe formed with at least a pair of detector electrodes disposed in theflow path, at least one detector electrode is formed on a substrate, thedetector electrodes carrying signals to the independent outputsrepresentative of the detected ion species, one detector electrode beingheld at a first level and the second detector electrode being held at asecond level for simultaneous detection of different ion species passedby the filter.

In an embodiment of the invention, the inlet section, ionizationsection, ion filtering section, and output section define between them aflow path for the flow of ions, further including a plurality ofelectrodes, including a pair of ion filter electrodes disposed in theflow path between the inlet section and output section. The plurality ofelectrodes may include an array of detector electrodes formed in theflow path.

In an embodiment of the invention, the trajectory of an ion passingthrough the ion filter is regulated by control section, wherein theoutput section further includes a detector, the detector including aplurality of electrodes in sequence to form a segmented detector,downstream from the ion filter, its segments separated along the flowpath to detect ions spatially according to their trajectories.

In an embodiment of the invention, the inlet section, ionizationsection, ion filtering section, and output section define a flow path,further including a plurality of electrodes defined in the flow path toform an arrangement of electrodes, the plurality defining at least onefilter electrode associated with each substrate to form an ion filtersection. The system may further include a pair of substrates, whereinthe ion filter includes at least a pair of filter electrodes formed onthe substrates, the substrates having at least an insulated surfacealong the flow path located between the filter electrodes and the outputsection. The system may include a plurality of dedicated flow pathscommunicating with the output section, wherein the arrangement ofelectrodes includes an array of filter electrode pairs associated withthe dedicated flow paths. The system may include a plurality ofdedicated flow paths, wherein the arrangement of electrodes includes anarray of detector electrodes in the output part and in communicationwith the dedicated flow paths. The system may include an arrangement ofelectrodes includes at least one pair of detector electrodes, oneassociated with each substrate, wherein the input part further includesan ionization region and further including at least one electrode in theionization region. The arrangement of electrodes may form a segmenteddetector with several segments, each segment formed with at least oneelectrode on a substrate, the segments being formed in a longitudinalsequence along the flow path in the output part. The electronics partmay be configured to sweep the applied controlling signals through apredetermined range according to the species being filtered. Thesubstrates may form a device housing, the device housing supporting theinput part, flow path, output part, electrodes, and electronics part. Aflow pump can be used for drawing a gas sample through the flow pathfrom the input part to the output part. A third substrate may beprovided wherein the substrates are planar and define two flow paths. Inone practice, the input part includes an ionization source for theionization of gas samples drawn by the flow pump, further including asecond pump for recirculation of air in at least one flow path.

In an embodiment of the invention, a spacer is provided extending alonga longitudinal axis defining a flow path between the inlet section andoutput section and the ion filter disposed in the flow path andincluding a pair of spaced filter electrodes, the control sectionincluding an electrical controller for applying an asymmetric periodicvoltage across the ion filter electrodes and for generating a controlfield, the control field controlling the paths of ions traveling throughthe filter along the longitudinal axis toward the output section. Thespacer can cooperate with the electrodes to form a device housingenclosing the flow path. The outlet may further include a detectionarea, the spacer defining a flow path extension extending along thelongitudinal axis and connecting the input to the detection area, ionspassed by the filter traveling to the detection area for detection. Thedetection area may include at least a pair of detector electrodes,further including an isolation part separating the ion filter from thedetector, the isolating part isolating the control field from thedetector electrodes. The spacer may further define longitudinalextensions, the flow path extending between the longitudinal extensionsand extending along the spacer longitudinal axis. This embodiment mayfurther include a pair of substrates, the substrates cooperating withthe spacer for defining the flow path between the inlet and outlet, thesubstrates further defining the filter electrodes facing each otheracross the flow path. Preferably the substrates have insulating surfacesthat define an electrically insulated flow path portion between theinlet and the outlet, the outlet further including an ion detector. Inone alterative, the spacer is silicon and defines confining electrodesin the flow path, further including a detector downstream from the ionfilter for detecting ions traveling from the filter under control of theconfining electrodes. The outlet may further include a detector, thedetector formed with at least a pair of electrodes for detection of ionsin the flow path, wherein the controller further defines electronicleads for applying signals to the electrodes. It is further possiblewherein the outlet defines an array of detectors, the detectors formedeach with a pair of electrodes disposed in the flow path for detectionof ion species passed by the filter, or wherein the outlet includes adetector, the detector including a pair of ion detector electrodes,wherein the electronics part is further configured to simultaneouslyindependently enable detection of different ion species, the detectedions being representative of different detected ion species detectedsimultaneously by the detector, the electronics part including separateoutput leads from each detector electrode, or wherein the outletincludes a detector having a plurality of electrode segments, thesegments separated along the flow path to spatially separate detectionof ions according to their trajectories. The ion filter may include anarray of filters, each filter including a pair of electrodes in the flowpath. Preferably the flow path is planar, further including a source ofions at the inlet, a pump communicating with the flow path for drivingof the ions through the filter, and possibly including a heater, in theflow path, for heating the flow path and purging neutralized ions,wherein the heater may include a pair of electrodes, the electrodeshaving at least one additional function, and the heater electrodes mayinclude the ion filter electrodes. The electrical controller may beconfigured to selectively apply a current through the filter electrodesto generate heat.

In an embodiment of the invention, a pair of spaced substrates definesbetween them a flow path between the inlet and an output sections, theion filter disposed in the path, further including at least a pair ofspaced filer electrodes, the filter including at least one of theelectrodes on each substrate, the control section further including aheater for heating the flow path. In one practice, the pair of theelectrodes on the substrates is used as a heat source for the heater,the control section configured to deliver a heater signal to the heatersource. In one practice, a pair of spaced substrates defining betweenthem a flow path between the inlet and an output sections, the ionfilter disposed in the path, further including at least a pair of spaceddetector electrodes at least one of the detector electrodes on eachsubstrate, the control section further including a heater for heatingthe flow wherein the control section uses the detector electrodes as aheat source.

In an embodiment of the invention, the control function is a duty cyclecontrol function generated by the control section, a flow path extendingbetween the inlet and output sections, the ion filter disposed in theflow path, the control section selectively adjusting the duty cycle ofthe asymmetric periodic voltage with the duty cycle control function toenable ion species from the inlet section to be separated, with desiredspecies being passing through the ion filter for detection. In onepractice, the asymmetric periodic voltage is not compensated with a biasvoltage, further including a detector downstream from the ion filter fordetecting ion species that are passed by the filter.

In one embodiment of the invention, a method is provided for generatingmultiple data for characterizing a chemical species in a gas sample, ina system having a flow path that defines an ion inlet, an output, and anion mobility filter in the flow path between the inlet and the output,the filter passing ions flowing from the inlet to the output. Themethods has the steps of: separating a gas sample with a GC and eludingthe separated sample in a carrier gas to the ion inlet, ionizing thesample and applying a drift gas to the sample and carrying the ionizedsample to the ion filter, applying an asymmetric periodic voltage to theion filter for controlling the path of ions in the ionized sample whilein the filter, and passing species through the ion filter for detectionat the output part. The method may further include the steps of:adjusting the duty cycle of the asymmetric periodic voltage to enableion species to be separated according to their mobilities, and passingspecies through the filter according to the duty cycle for detection atthe output part.

In another embodiment of the invention, a method is provided foranalysis of compounds in chromatography, including the steps of:separating chromatographically a gas mixture to be analyzed in achromatographic column, ionizing the gas mixture, passing the ionizedgas to a field asymmetric ion mobility spectrometer and passingcomponents of the separated mixture through a high field asymmetric ionmobility filter, and detecting ions in the mixture according to theirmobilities. The method may further include the step of applying a driftgas to the eluted sample to increase the flow volume and velocity of theions through the spectrometer. The sample is eluted from the outlet of acapillary column of a GC, and a further step includes surrounding thecapillary column outlet with the flowing drift gas. The method also mayinclude the step wherein the system has an ionizer for ionizing thesample and creating reactant ions, the reactant ions reacting with theionized sample to create reactant ion data peaks, further including thestep of obtaining GC retention time by monitoring the fluctuation inintensity of the reactant ion data peaks. Furthermore, the method mayinclude the steps of detecting positive and negative ions simultaneouslyby passing ions at high RF. The system has an ionizer for ionizing thesample, and a further step includes processing detection data andobtaining retention time, compensation voltage and intensity, andrelating this to the sample to identify its species.

In another embodiment of the invention, a sensor system forcharacterizing a chemical species in a gas sample, includes an inletsection, an ionization section, an ion filtering section, an outputsection for ion species detection, a control section, and a section forgas chromatographic (GC) analysis of a gas sample, the GC sectioncoupled to the inlet section, and the ionization section disposed forionizing a gas sample from the GC section, the ionized sample passing tothe ion filter section, the control section applying a high fieldasymmetric period voltage and a control function to the ion filter tocontrol species in the sample that are passed by the filter to theoutput section for detection, a planar housing defining a flow pathbetween a sample input part and an output part, the housing formed withat least a pair of substrates that extend along the flow path, an ionfilter disposed in the flow path, the filter including at least one pairof filter electrodes, at least one on each substrate across from eachother on the flow path, and the control section having a control partconfigured to apply an asymmetric periodic voltage to the ion filterelectrodes for controlling the travel of ions through the filter.

The following detailed description is directed to embodiments of methodsand apparatus for chromatographic high field asymmetric waveform ionmobility spectrometry for analysis of compounds. It will be appreciatedthat in practice of the invention, filtering is achieved by accentuatingdifferences in ion mobility. The asymmetric field alternates between ahigh and low field strength condition which causes the ions to move inresponse to the field according to their mobility. Typically themobility in the high field differs from that of the low field. Thatmobility difference produces a net displacement of the ions as theytravel in the gas flow through the filter. In absence of a compensatingbias signal, the ions will hit one of the filter electrodes and will beneutralized. In the presence of a specific bias signal, a particular ionspecies will be returned toward the center of the flow path and willpass through the filter. The amount of change in mobility in response tothe asymmetric field is compound-dependent. This permits separation ofions from each other according to their species, in the presence of anappropriately set bias.

It will now be appreciated that in practice of the present inventionthat the terms detector, spectrometer and sensor have specific meanings.However, these terms also may be used interchangeably from time to timewhile still remaining within the spirit and scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully understood by reference to the following detailed descriptionin conjunction with the attached drawing in which like referencenumerals refer to like elements and in which:

FIG. 1 is a is a cross-sectional schematic view of a prior art FIS/FAIMSSpectrometer.

FIG. 2(a) is a system level schematic of the GC-PFAIMS of the invention.

FIG. 2(b) is a more detailed schematic of an embodiment of the oneconfiguration of the coupling of the GC column with the PFAIMS.

FIG. 2(c) another schematic of a GC-PFAIMS where ionization source isnot completely inside of flow channel.

FIG. 2(d) another schematic where the ionization is done prior tointroduction of the sample from the GC column.

FIG. 3(a) is a perspective view of a PFAIMS embodiment of the invention.

FIG. 3(b) is a side cross-sectional view of the embodiment of FIG. 3(a)showing the spacers and spaced substrates.

FIG. 3(c) exploded perspective view of an alternative embodiment of theinvention using insulating spacers.

FIGS. 4(a,b) are schematic views of arrays of filter and detectorelectrodes in a single flow path.

FIG. 5 is an exploded view of an array of filters with multiple flowpaths.

FIG. 6 is a schematic of a multi-layer PFAIMS in practice of theinvention.

FIG. 7 is a schematic of segmented detector electrodes in practice ofthe invention.

FIG. 8 experimental data comparing the detection limits of the PFAIMSwith an industry standard Flame Ionization Detector (FID).

FIG. 9 shows GC-PFAIMS spectra for a homologous alcohol mixture.

FIG. 10 Comparison of the reproducibility of the PFAIMS with a Flameionization detector. The two graphs show comparable reproducibilityperformance.

FIG. 11(a) GC-PFAIMS spectra.

FIG. 11(b) Illustration of the reactant ion peak and effect of itsinteraction with a product ion.

FIG. 12 Simultaneously obtained spectra for positive and negative ionsusing the PFAIMS as the detector.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention provides methodology and apparatus for theanalysis of compounds by gas chromatography high field asymmetricwaveform ion mobility spectrometry. In a preferred embodiment of theinvention, a GC-PFAIMS chemical sensor system 10, shown in FIG. 2(a),includes a gas chromatograph (GC) separation section 10A intimatelycoupled to a planar high field asymmetric ion mobility spectrometer(PFAIMS) section 10B, and enabled by a data and system controllersection 10C. The data and system controller both controls operation ofsystem 10 and appraises and reports detection data.

In practice of a preferred embodiment of the present invention, as shownin FIG. 2(b), the GC section 10A includes a capillary column 11 thatdelivers a carrier gas sample 12 a (with compounds), eluting from the GCaccording to solubility, to the inlet 16 of the PFAIMS spectrometersection 10B. A drift gas 12 c (which may be heated) is also introducedinto the inlet 16 via a passageway 11 a that surrounds column 11. Thisdrift gas is at a volume as required to carry the ions through thespectrometer. The flow rate of the drift gas is controlled to ensurereproducible retention times and to minimize detector drift and noise.The compounds/carrier gas 12 a and drift gas 12 c are subjected toionization in ionization region 17 via an ion source or ionizer 18(e.g., radioactive, corona discharge, etc.). In this embodiment, thecarrier and drift gases are under positive pressure, however a pump 14may be employed to draw the gas sample into ionization region 17 and todraw the ionized gas along flow path 26. In any event, the gas and thecompound sample is driven or drawn along the flow path between theparallel electrode plates 20, 22 of ion filter 24, while subjected to ahigh intensity asymmetric waveform radio frequency (RF) signal 40 and acompensation signal 41, as applied to the filter electrodes by RF/DCgenerator circuits 28 under direction of controller 30.

The output part 31 includes detector 32. As ions pass through filter 24,some are neutralized as they collide with the filter electrodes, whileothers pass to detector 32. The data and system controller 10C regulatesthe signal on the filter electrodes, thus regulating which ion speciespass through the filter. Controller 10C drives the detector electrodesand receives, interprets and displays their outputs.

An alternative embodiment of the present invention is shown in FIG. 2(c)where GC section 10A includes a GC column 11 coupled to PFAIMSspectrometer 10B at inlet 16, ionized samples pass through filter 24 tothe detector region 31. The detector region 31 could couple directly toa mass spectrometer 82 or other detector. The ionization source can beincluded entirely, partially, or external to the drift tube withpossibly an opening in the ionization region drift tube for the gassample to interact with the ionization source. The connection betweenthe GC and the FAIMS is preferably through a T-connector which screwsinto both the GC outlet and the PFAIMS inlet housing and allows the GCcolumn to be passed through it to deliver the carrier gas and sampleinto the ionization region. The T-connector serves to protect the GCcolumn. It also receives and delivers the drift gas to the PFAIMS.

In yet another embodiment of the present invention, shown in FIG. 2(d),a GCP-FAIMS system includes an ionization source 18′ (which can beremote) for ionization, wherein the drift gas 12 c is introduced throughionization region 17 to the PFAIMS filter section 24, while the elutedsamples 12 a from the GC Column enter after the ionization region to amixing region 17′. Resulting product ions 42′ are flowed into the filter24.

In an embodiment of this device, reactant ions 17″ are created throughthe ionization of the drift gas 12 c, and then they are mixed with thesample 12 a coming from the GC column in the mixing region 17′ to createthe desired product ions 42′ from the sample 12 c. The advantage of thisdesign is that the sample molecules do not see the ionization source andcannot react with it, as some chemicals introduced by the GC may attackthe ionization source. Using this design, many additional chemicalswhich ordinarily cannot be used with a particular ionization source canbe used herein.

Coupling of a GC with a FAIMS is non-trivial, since the flow rates ofthe compounds eluted from a conventional GC are too slow to match therequired flow rate in the conventional FAIMS. It is known that iontrajectories are highly dependent upon gas flow rate. Simply couplingthe GC (GC column) with the FAIMS would result in no ions reaching thedetector region, because of massive neutralization at the filterelectrodes.

In practice of an embodiment of the invention, for appropriate functionof the filter 24 of PFAIMS section 10B, the ions need to travel at acertain velocity (e.g., around 6 meters per second for an ion filter 15millimeters long). The gas flow velocity defines the ion velocitythrough the filter. The average velocity of the gas in the ion filterregion can be defined as V=Q/A, where Q is the gas volume flow rate andA is the cross-sectional area of the channel. In one example, the PFAIMShas a cross-sectional area A=5×10E-6 m². Therefore a flow rate Q=2liters per minute of gas is required to produce roughly 6 meters persecond average velocity for the ions through the filter, for example. Ifthe ion velocity is less than V=6 meters per second for this device noions will make it through the filter and they will all be deflected tothe ion filter electrodes and be neutralized.

Typical flow rates of the GC sample eluting from the column are in themilli-liters per minute range, too slow for direct introduction anddetection in a PFAIMS. Thus a novel design is required to accommodatethe interface. Preferably a supplementary drift gas is added to augmentthe sample flow from the GC column, which makes the GC-PFAIMS approachviable.

By controlling the flow rate of the carrier gas in the GC column (or theratio of carrier gas to sample) relative to the volume flow rate of thedrift gas, various dilution schemes can be realized which will increasethe dynamic range of the PFAIMS detector (see for example FIG. 2(c)). Ifthe PFAIMS must detect a high concentration of sample it is desirable todilute the amount of this sample in a known manner so that the PFAIMScan do the detection in its optimal sensitivity regime.

In a preferred embodiment, the ion filter is formed on the insulatingsurfaces of the substrates. The benefit of being able to lay downelectrodes on a planar insulating surface is that it lends itself tocompact packaging and volume manufacturing techniques. As such, the ionfilter is defined on these insulated surfaces by the filter electrodes,facing each other over the flow path, while the insulated surfaces ofthe substrates, such at region X, isolate the control signal at thefilter electrodes from the detector electrodes for lower noise andimproved performance.

It will be appreciated that embodiments of the GC-PFAIMS inventionfeature a multi-functional use of the PFAIMS substrates. The substratesare platforms (or a physical support structures) for the precisedefinition and location of the component parts or sections of theGC-PFAIMS device. The substrates form a housing, enclosing the flow pathwith the filter and perhaps the detector, as well as other componentsenclosed. This multi-functional design reduces parts count while alsoprecisely locating the component parts so that quality and consistencyin volume manufacture can be achieved. The smaller device also hasunexpected performance improvements, perhaps because of the shorterdrift tube and perhaps also because the substrates also perform anelectronic isolation function. By being insulating or an insulator(e.g., glass or ceramic), the substrates also can be a direct platformfor formation of components, such as electrodes, with improvedperformance characteristics.

The GC-PFAIMS sensor with insulated substrate/flow path achievesexcellent performance in a simplified structure. The use of anelectrically insulated flow path in a GCPFAIMS device enables theapplied asymmetric periodic voltage (which is characteristic of a PFAIMSdevice) to be isolated from the output part (e.g., from the electrodesof the detector), where detection takes place. This reduction isaccomplished because the insulated substrates provide insulatedterritory “x” FIG. 2(b), between the filter and detector in the flowpath, and this spacing in turn advantageously separates the filter'sfield from the detector. The less noisy detection environment means amore sensitive PFAIMS device and therefore a better GC-PFAIMS sensor.Sensitivity of parts per billion and possibly parts per trillion can beachieved in practice of the disclosed invention.

Moreover, by forming the electrodes on an insulative substrate, the ionfilter electrodes and detector electrodes can be positioned closertogether which unexpectedly enhances ion collection efficiency andfavorably reduces the device's mass that needs to be regulated, heatedand controlled. This also shortens the flow path and reduces powerrequirements. Furthermore, use of small electrodes reduces capacitancewhich in turn reduces power consumption. As well, depositing the spacedelectrodes lends itself to a mass production process, since theinsulating surfaces of the substrates are a perfect platform for theforming of such electrodes. This may be performed on a single chip.

It is further noted that use of the substrates as a support/housing doesnot preclude yet other “housing” parts or other structures to be builtaround a GC-PFAIMS device. For example, it might be desirable to put ahumidity barrier over the device. As well, additional components, likebatteries, can be mounted to the outside of the substrate/housing, e.g.,in a battery enclosure. Nevertheless, embodiments of the presentlyclaimed GC-PFAIMS invention stand over the prior art by virtue ofperformance and unique structure generally, and the substrate insulationfunction, support function, multi-functional housing functions,specifically, as well as other novel features.

One embodiment of the PFAIMS device (with GC removed) is shown in FIG.3(a), where it will be appreciated that the substrates cooperate to forma planar housing 13. This multi-use, low parts-count housingconfiguration enables smaller real estate and leads to a smaller andmore efficient operating PFAIMS device, perhaps as small as 1″×1″×1″.

Preferably the Spectrometer section 10B is formed with spaced insulatedsubstrates 52, 54, (e.g., Pyrex® glass, Teflon®, pc-board) having thefilter electrodes 20, 22 formed thereon (of gold, platinum, silver orthe like). The substrates 52, 54 further define between themselves theinput part 16 and output part 31, along flow path 26. Preferably outputpart 31 also includes the detector 32, with the detector electrodes 33,35 mounted on insulated surfaces 19, 21, facing each other across theflow path.

Pump 14 generates the air flow, and along with the compact structurehousing/substrate structure, enables a very compact PFAIMS device. Pump14 a can be used for recirculation for supply of conditioned air to theflow path.

FIG. 3(b) is front cross-sectional view of one embodiment of a PFAIMSwhere electrodes 20 and 22 are formed on insulating substrates 52 and54. Either insulating or conducting spacers 56 a and 56 b serve toprovide a controlled gap between electrodes 20 and 22 and define theflow path.

Ion filter 24 passes selected ions according to the electric signal onthe filter electrodes. The path taken by a particular ion is a functionof its species characteristic, under influence of the applied electricsignals. In practice of one embodiment of the invention, the asymmetricelectric signal is applied in conjunction with a compensating biasvoltage 44, and the result is that the filter passes desired ion speciesaccording to control signals supplied by an electronic controller 30. Bysweeping bias voltage 44 over a predetermined voltage range, a completespectrum for sample gas 12 can be achieved. In another embodiment, theasymmetric electric signal enables passing of the desired ion specieswhere the compensation is in the form of varying the duty cycle of theasymmetric electric signal, without the need for compensating biasvoltage, again under direction of the control signals supplied by theelectronic controller 30.

In another embodiment substrates 52, 54 are separated by spacers 56 a,56 b, which may be formed by etching or dicing silicon wafers, but whichmay also be made of patterned Teflon, ceramic, or other insulators. Thethickness of spacers 56 a, 56 b defines the distance between thesubstrates and electrodes 20, 22. In one embodiment, these spacers areused as electrodes and a confining voltage is applied to the siliconspacer electrodes to confine the filtered ions within the center of theflow path. This confinement can result in more ions striking thedetectors, and which in turn improves detection.

In another embodiment as shown in the exploded view of FIG. 3(c)structural electrodes 20 x and 22 x are separated by insulating spacers56 a, 56 b, and the flow path 26 is formed therewithin. At one end aninput part 11 x supplies the ions to the filter 24 x, and at the otherend the filtered ions pass into an output part 31 x.

In operation of the PFAIMS spectrometer 10B, some ions will be driveninto the electrodes 20, 22 and will be neutralized. These ions can bepurged by heating. This may be accomplished in one embodiment by heatingthe flow path 26, such as by applying a current to filter electrodes 20,22, or to spacer electrodes 56 a, 56 b. As heater electrodes, they alsomay be used to heat the ion filter region to make it insensitive toexternal temperature variations.

The devices of the invention have various electrode arrangements,possibly including pairs, arrays and segments. Filtering may include thesingle pair of filter electrodes 20, 22 (FIG. 2). But device performancemay be enhanced by having a filter array 62 (e.g., FIGS. 4-5). It willbe appreciated that FIGS. 4(a,b) has multiple filters (i.e., an array)in a single flow channel, and FIG. 5 has multiple flow channels, eachwith at least a single filter or an array.

The filter array 62 may include a plurality of paired filter electrodes20 a-e and 22 a-e and may simultaneously pass different ion species bycontrol of the applied signals for each electrode pair. In addition, itis possible to sweep the control component for each pair over a voltagerange for filtering a spectrum of ions.

Further, with an array of filters, a complete spectral range ofcompensation voltages can be more rapidly scanned than with a singlefilter. In an array configuration, each filter can be used to scan overa smaller voltage range. The combination of all of these scans resultsin sweeping the desired full spectrum in a reduced time period. If thereare three filters, for example, the spectrum can be divided into threeportion and each is assigned to one of the filters, and all three can bemeasured simultaneously.

In another mode, filter array 62 may include paired filter electrodes 20a-e and 22 a-e and may simultaneously enable detection of different ionspecies by applying a different compensation bias voltage 44 to eachfilter of the array, without sweeping. In this case, only an ion speciesthat can be compensated by this fixed compensation voltage will passthrough each filter, and the intensity will be measured. In practice ofthe invention, array 62 may include any number of filters depending onthe size and use of the spectrometer.

The filter array 62 may have one common flow path 26 or individual flowpaths 26 a-e (FIG. 5). For each flow path, this may include anindependent component set, such as for example inlet 16 a, ionizationregion 18 a, confining electrodes 56 a′, 56 b′, ion filter electrodepair 20 a, 22 a, detector electrode pair 33 a, 35 a, and exit port 68 a,that may detect a particular ion species while other species are beingdetected. Having multiple channels provides additional information andadditional flexibility in the sampling process.

As will be appreciated by those skilled in the art, different specieshave different affinities to different dopants, and therefore inpractice of an embodiment of the invention having an array ofelectrodes, multiple flow paths can be provided and each flow path canbe doped with a different dopant. The result is that the ion filters anddetectors can be specialized for a selected species and now furtherspecialization of the flow paths result in enhanced discriminationcapability.

Use of arrays is important when there is a desire to measure perhaps adozen or so compounds in a very short amount of time. If a fast GC isused as the front end to a PFAIMS, the widths of the chemical peakseluting from the GC can be as short as a few seconds. In order to obtaina complete spectral sweep over the required compensation voltage rangein time to capture the information contained in the GC the spectralrange can be subdivided amongst the ion filters in the array. Thisallows a simultaneous detection of all the constituents in the given GCpeak.

In further practice of the invention, detector 32 can detect single ormultiple species at the same time. In one embodiment, a detector 32includes a top electrode 33 at a predetermined voltage and a bottomelectrode 35 at another level, perhaps at ground. Top electrode 33deflects ions of the correct polarity downward to electrode 35 and aredetected thereat. This arrangement is shown in FIG. 6, for example, butis not limited to this configuration.

The design of FIG. 6 has several advantages under particular sampleanalysis conditions. The PFAIMS device described in FIG. 6 has two flowpaths 26′, 26″. The sample 12 eluting from the GC column enters inlet 16and is ionized at ionization region 17 in Region 1, flow path 26′. Inthis embodiment, electrodes 18 provide ionization in this region.

The embodiment of FIG. 6 might also have a different detectorarrangement, such as a single electrode, a deflector electrodes, an MS,or other schemes, within the scope of the invention.

The ions pass between steering electrodes 56 ax, 56 bx and flow intoRegion 2, flow path 26″, which may contain filtered or conditioned gas.The balance of the flow is exhausted out the gas exhaust 16 x in Region1 along flow path 1. Once introduced into the ionization region 17, thesample molecules are ionized and these ions 42′ are steered byelectrodes 56 ax, 56 bx and flow into flow path #2 where they travelthrough the ion filter electrodes 20, 22 are detected at detector 32.According to ion mobility and the applied voltages, ions 42″ pass to thedetector 32. The gas is exhausted and may be cleaned, filtered andpumped at handler 43 and returned as clean filtered gas 66 back into theflow path 2 of Region 2.

There are several advantages of this design. Firstly, this design allowsfor independent control of the flow rates in flow path #1 and #2,provided the pressures are balanced at the open region between flow path#1 and #2. This means that a higher or lower flow rate of the sample canbe used, depending on the particular GC system, while the flow rate ofthe ions through the ion filter can be maintained constant allowing,consistent, reproducible results. If the flow rate through the ionfilter had to be changed due to the sample introduction system thiswould adversely effect the PFAIMS measurement. The efficiency of the ionfiltering would be impacted and the location of the peaks (compensationvoltages) in the PFAIMS spectrometer would be different at the differentflow rates. This in turn would require different high voltage highfrequency fields to be used which would make for a complicatedelectronics system.

A second advantage is that the ion filter region can be kept free ofneutrals. This is important when measuring samples at highconcentrations coming out of the GC column. Because the amount of ionsthe ionization source can provide is fixed, if there are too many samplemolecules, some of the neutral sample molecules may cluster with thesample ions and create large molecules which do not look at all like theindividual sample molecules. By injecting the ions immediately into theclean gas flow in flow path #2, and due to the effect of the highvoltage high frequency field, the molecules will de-cluster, and theions will produce the expected spectra

A third advantage is that the dynamic range of the PFAIMS detector isextended. By adjusting the ratios of the drift gas and GC-sample/carriergas volume flow rates coming into ionization region 17 (FIG. 6) theconcentration of the compounds eluting from the GC can becontrolled/diluted in a known manner so that samples are delivered tothe PFAIMS ion filter 24 at concentrations which are optimized for thePFAIMS filter and detector to handle. In addition steering electrodes 56ax, 56 bx can be pulsed or otherwise controlled to determine how manyions at a given time enter into Region 2.

Region 1 in FIG. 6 may also contain ion filter 24 x in Region 1. In thisarrangement, parallel PFAIMS devices are presented, where filter 24 xhas electrodes 20′, 22′, in Region 1, as shown in phantom, and possiblyalso detector 32 x having electrodes 33′, 35′, in phantom.

In this embodiment, different gas conditions may be presented in each.With a suitable control applied to the two steering electrode 56 ax, 56bx selection can be made as to which region the ions are sent. Becauseeach chamber can have its own gas and bias condition, multiple sets ofdata can be generated for a single sample. This enables improved speciesdiscrimination in a simple structure, whether or not a GC is used forsample introduction.

The electronics controller 30 supplies the controlling electronicsignals. A control circuit could be on-board (e.g., FIG. 3), oroff-board, where the GC-PFAIMS device 10 has at least the leads andcontact pads that connect to the control circuit (e.g., FIGS. 4-6). Thesignals from the controller are applied to the filter electrodes viaelectric leads 71, such as shown on the substrate in FIG. 4.

Electronic controller 30 may include, for example, amplifier 34 andmicroprocessor 36. Amplifier 34 amplifies the output of detector 32,which is a function of the charge collected on electrode 35 and providesthe output to microprocessor 36 for analysis. Similarly, amplifier 34′may be provided where electrode 33 is also utilized as a detector. Thus,either electrode may detect ions depending on the ion charge and thevoltage applied to the electrodes; multiple ions may be detected byusing top electrode 33 as one detector at one polarity and bottomelectrode 35 as a second detector at the other polarity, and using thetwo different amplifiers. Thus the GC-PFAIMS sensor of the invention mayachieve multiple simultaneous detections of different ion species.

Furthermore, detector array 64 may be provided with detectors 32 a-e todetect multiple selected ions species simultaneously, providing fasterperformance by reducing the time necessary to obtain a spectrum of thegas sample (FIG. 4).

In one further embodiment, to improve the GC-PFAIMS device resolution,detector 32 may be segmented, as shown in FIG. 7. As ions pass throughfilter 24 between filter electrodes 20 and 22, the individual ions 38c′-38 c″″ may be detected by spatial separation, the ions having theirtrajectories 42 c′-42 c″″ determined according to their size, charge andcross-section. Thus detector segment 32′ will have a concentration ofone species of ion while detector segment 32″ will have a different ionspecies concentration, increasing the spectrum resolution as eachsegment may detect a particular ion species.

The GC-PFAIMS device is small and compact, with minimized capacitanceeffects owing to the insulated substrates. In a preferred embodiment,devices in practice of the invention are able to rapidly produceaccurate, real-time or near real-time, in-situ, orthogonal data foridentification of a wide range of chemical compounds.

The benefits of the simplified GC-PFAIMS sensor system according to theinvention requires typically as little as a fraction of a second toproduce a complete spectrum for a given gas sample. This has not beenachieved before in any GC-FAIMS combination chemical sensor system.

In one practice of the invention, the PFAJMS has a small size and uniquedesign which enable use of short filter electrodes that minimize thetravel time of the ions in the ion filter region and thereforeniinixnize the detection time. The average ion travel time td from theionization region to the detector is determined by the draft gasvelocity V and the length of the ion filter region Lf, and is given bythe relation td=Lf/V. Because Lf can be made small (e.g., 15 mm or less)in our device, and the RF asymmetric fields can have frequencies as highas 5 megahertz, the response time of the PFALMS can be very short (aslittle as one millisecond, while the ion filtering (discrimination) canstill be very effective. P The presently disclosed PFAIMS has beendemonstrated to be capable of generating complete field asymmetric ionmobility spectra of the compounds in a single GC peak in both regular GCand fast GC. This is not possible in prior FAIMS devices. For example,the FIS (FAIMS developed by MSA) features a cylindrical design, theelectric fields are non-uniform and ion focusing occurs. For the ionfocusing to be effective, a significantly longer ion filter regionlength, Lf is required, making the travel time td of the ion much longer(by as much as, or even more than 10-100 times longer than the presentlydisclosed PFAIMS). This prevents the FIS from generating a completespectral scan of the compounds contained within a single GC peak.

Again, only the present PFAIMS invention is capable of generating acomplete FAIMS spectra of the compounds in a single GC peak in bothregular GC and fast GC. In part this is due to the fact that the smallsize of the GC-PFAIMS enables ion residence times as low as onemillisecond (one thousandth of a second), i.e., the time to travel fromthe ionizer to the detector in the PFAIMS section. A total spectra(e.g., sweeping the bias over a range of 100 volts) can be obtained inunder one second. This makes the speed of ion characterizationcomparable to that of a modern quadrupole mass spectrometer, but withoutthe MS limitation of operation in a vacuum. The PFAIMS rapid detectionnow enables combination with a GC and results in a highly capablechemical detection system that can exploit the full capability of theGC.

This system in practice of the invention even can be operated in a fastGC mode that the prior FIS could not keep up with. In this mode thePFAIMS generates a complete spectra of the ions under the GC peaks, andgenerates enough data to enable 2- and 3-dimensional graphicalrepresentation of the data as shown in FIG. 2. The result of the 2 and3-D plots are fast, high accuracy identification of the compounds beingdetected. This is an important advantage of the present invention andleads to exceptionally meaningful chemical detections andcharacterizations.

The short length of the PFAIMS spectrometer section 10B and smallionization volume mean that the GC-PFAIMS provides the ability to studythe kinetics of ion formation. If the ions are transported very rapidlythrough the PFAIMS section, the monomer ions are more likely to be seensince there is less time for clustering and other ion-moleculeinteractions to occur. By increasing the ion residence time in thePFAIMS section, the ions have more opportunity to interact with otherneutral sample molecules forming clusters and the final product ionswhich tend to be diamers (an ion with a neutral attached). Thereforesize and speed can be favorably controlled in practice of the invention.

Ion clustering can also be affected by varying the strength (amplitude)of the high field strength asymmetric waveform electric field. Byapplying fields with larger amplitudes or at higher frequencies theamount of clustering of the ions can be reduced, representing yetanother means of enhanced compound discrimination.

In practice of the invention, a GC-PFAIMS system was formed as follows:A model 5710 gas chromatograph (Hewlett-Packard Co., Avondale PA) wasequipped with a HP splitless injector, 30 m SP 2300 capillary column(Supelco, Bellefonte, Pa.), columns as short as 1 m have also been used,and a PFAIMS detector. Air was provided to the GC drift tube at 1 to 2 1min-1 and was provided from a model 737 Addco Pure Air generator (Miami,Fla.) and further purified over a 5 Å molecular sieve bed (5 cmdiameter×2 m long). The drift tube was placed on one side of an aluminumbox which also included the PFAIMS electronics package. A 10 cm sectionof capillary column was passed through a heated tube to the PFAIMS. Thecarrier gas was nitrogen (99.99%) scrubbed over a molecular sieve bed.Pressure on the splitless injector was 10 psig and the split ratio was200:1.

The compensation voltage was scanned from +/−100 Vdc. The asymmetricwaveform had a high voltage of 1.0 kV (20 kV cm-1) and a low voltage of−500 V (−5 kV cm-1). The frequency was 1 MHz and the high frequency hada 20% duty cycle, although the system has been operated with frequenciesup to 5 MHz in practice of the invention. The amplifier was based upon aAnalog Devices model 459 amplifier and exhibited linear response timeand bandwidth of 7 ms and 140 Hz, respectively. Signal was processedusing a National Instruments board (model 6024E) to digitize and storethe scans and specialized software to display the results as spectra,topographic plots and graphs of ion intensity versus time. The ionsource was a small 63Ni foil with total activity of 2 mCi. However, asubstantial amount of ion flux from the foil was lost by the geometry ofthe ionization region and the estimated effective activity is 0.6 to 1mCi.

The GC-PFAIMS sensor is a relatively inexpensive, fast, highlysensitive, portable chemical sensor. The GC-PFAIMS combines some of thebest features of a flame ionization detector with those of a massspectrometer. However, the average PFAIMS detection limits areapproximately an order of magnitude better than those of FID. FIG. 8compares FID and PFAIMS response as a function of compound concentrationfor a homologous Ketone mixture. (Note average FID detection limit is2E-10g, while average PFAIMS detection limit is 2E-11g.)

Similarly to a mass spectrometer, the information provided by theGC-PFAIMS scans offers the ability to obtain unambiguous compoundidentification. FIG. 9 is a GC-PFAIMS chromatogram (right frame) andconstitutes the sum of the peak intensities for the product ionscreated. This same data could be generated using an FID. In theGC-PFAIMS, the chromatogram represents only a part of the generateddata. Unlike the FID, there is also an associated two-dimensional plot(left frame) of ion intensity, as indicated by the gradient, versuscompensation voltage generated by the PFAIMS scans. This combination ofdata provides a means of fingerprinting the compounds eluted from the GCin the presently disclosed GC-PFAIMS sensor system.

The present GC-PFAIMS invention enjoys unforeseen advantages. TheGC-PFAIMS provides three levels of information: retention time,compensation voltage, and ion intensity. Furthermore, both positive andnegative spectra are obtained simultaneously, eliminating the need forserial analysis under different instrumental conditions (as required inMS). The wealth of information provided by the GC-PFAIMS, in some cases,eliminates the need of external calibration through standards.

In the field, or under particular conditions, such as environmentalconditions, variable humidity or sample concentrations, the retentiontimes of compounds may shift from their expected values. When analyzingan unknown complex mixture, this is a serious problem. In order tocorrect for this shift, a known standard, at a known concentration, isrun through the GC first to calibrate the GC. Running a standardhowever, takes time and adds complexity; furthermore, the standard is aconsumable, and is inconvenient to use in the field. Because the PFAIMSprovides a second dimension of information, even though the GC retentiontime for the different compounds may shift, the additional informationprovided by the PFAIMS spectra can provide an accurate identification ofthe compound without the need of a standard. Reproducibility of thePFAIMS spectrometer compares favorably to that of the FID as shown inFIG. 10 (a comparison of the reproducibility of the PFAIMS versus FID).

The left frame display of information, such as in FIG. 11a, is unique tothe presently disclosed PFAIMS spectrometer 10B. To date, no one hasdisplayed a 2-dimensional plot of compensation voltage versus retentiontime for discrimination of ion species.

The spectra on the right is a total ion intensity measure generated bysumming all the ions in the spectra from the left frame at a givenretention time. This can be done in two ways. Either by summing theintensities of all the spectra in software, or else, if an ionizationsource which produces a reactant ion peak (example of sources areradioactive and corona discharge sources) is used, then by monitoringthe changes in the intensities of the reactant ion peak.

The GC-PFAIMS advantageously features the ability to obtain theretention time spectra by monitoring changes in intensity of theReactant Ion Peak (RIP peak). This further enables the ability toprovide a chemical sensor that is able to rapidly produce accurate,orthogonal data for identification of a range of chemical compounds.Quite beneficially, the overall attributes of the GC-PFAIMS results insimple analytical protocols that can be performed by untrainedpersonnel, with faster sample analysis at lower cost.

More specifically, the reactant ion peak is a chemical peak produced bythe ionization of the “background” air (carrier gas), molecules such asnitrogen and water molecules, and produces a fixed intensity ion signalat the detector at a particular compensation voltage. The intensity ofthe reactant ion peak is determined by the activity (energy) of theionization source. As illustrated in the FIG. 11b, the reactant ion peakoccurs at a particular compensation voltage. When an organic compound iseluted from the GC some charge is transferred from the reactant ioncompounds to this compound creating what is called a product ion. Theformation of the product ion results in a decrease in the intensity ofthe reactant ion peak (amount of reactant ions available). The amount ofdecrease in the reactant ion peak intensity is equal to the amount ofions required to create the product ions. If multiple product ions areproduced at the same time the reactant ion peak intensity will decreasein the amount equal to the intensity of the product ions intensitiescombined. In other words, by monitoring the changes in the reactant ionpeak the same information can be obtained as summing all of theindividual product ion peaks.

The present PFAIMS features the ability to measure both positive andnegative ions simultaneously. Unlike a mass spectrometer or an IMS forexample, the PFAIMS allows the simultaneous detection of both positiveand negative ions, such as where detector electrodes 33 and 35 are eachrun as independent outputs to the data system.

The GC-PFAIMS spectra for an insect pheromone mixture is shown in FIG.12, where positive and negative spectra are obtained simultaneously fromthe PFAIMS while analyzing a mixture of pheromone simulants. Notice thatunder GC peak 2 and 4 we have both anion and cations present. Thepositive and negative spectra are obtained simultaneously, eliminatingthe need of serial analysis under different instrumental conditions, asrequired in MS.

Simultaneous detection cuts down on analysis time, since only one scanis required to obtain multiple species detection. Also it provides amuch richer information content compared to TOF-IMS, so that one can geta better identification of the ion species being detected. For example,in FIG. 12, the entire measurement took approximately 800 seconds to seeall of the GC peaks in the sample. If we were to repeat this experimentfor the negative (anions) we would have to wait another 800 seconds. Itis also important when limited samples are available and measurementscan only be performed once.

Embodiments of the claimed invention result in GC-PFAIMS devices thatachieve high resolution, fast operation and high sensitivity, yet with alow parts count and in configurations that can be cost-effectivelymanufactured and assembled in high volume. Quite remarkably, packagingis very compact for such a capable device, with sensitivity in the rangeof parts per billion or trillion. In addition, the reduced real estateof this smaller device leads to reduced power requirements, whether insensing ions or in heating the device surfaces, and can enable use of asmaller battery. This reduced power requirement and size can be veryimportant in fielding portable devices, such as in fielding a portablechemical sensor, for example, made in practice of the invention.

It will therefore be appreciated by a person skilled in the art that theclaimed invention provides the possibility of a small GC-PFAIMS devicewith low parts count, with parts that themselves are simplified indesign. Thus the device can be volume-manufactured with conventionaltechniques and yet with high production yields. The simplicity of thestructure also quite remarkably leads to favorable performance. Theresult is a compact, low-cost device with high quality and performance.

Nothing like the claimed invention has been disclosed or achieved in thepast. The novel breakthrough of the present invention, in one aspect,can be attributed to providing a multi-use housing/substrate structurethat simplifies formation of the component parts. Additional featuresinclude the possibility to use the substrate as a physical platform tobuild a GC receiver in proper alignment with an ionizer, and further tobe able to build the filter and detector on the substrate. In short, tobe able to give structure to the whole device, to use the substrate asan insulated platform or enclosure that defines the flow path throughthe device, and/or to be able use the substrate to provide an isolatingstructure that improves performance. Multiple electrode formations, anda functional spacer arrangement are also taught, which again improveperformance and capability.

In practice of the GC-PFAIMS apparatus of the invention, filteringemploys the asymmetric period voltage applied to the filters along witha control component, and this component need not be a bias voltage butmay be supplied simply by control of the duty cycle of the sameasymmetric signal. A spacer can be incorporated into the device, whichprovides both a defining structure and also the possibility of a pair ofsilicon electrodes for further biasing control. Finally, this compactarrangement enables inclusion of a heater for purging ions, and may eveninclude use of the filter or detector electrodes for heating/temperaturecontrol.

In application of the present invention, a convenient portable GC-PFAIMSchemical sensor can be provided for the detection of specific compoundsin a gas sample. Substances that can be detected can include traces oftoxic gases or traces of elements contained in drugs or explosives, forexample. Presently, mass spectrometers are known that can providerelatively quick and accurate detections with high resolution and goodsensitivity, but mass spectrometers are both expensive and large. Yetthe need is great to be able to have a proliferation of portable sensorsin desired locations (whether on the battlefield, at an airport, or in ahome or workplace), and so there is a felt need for lower cost, massproducible, portable devices that enable high quality performance. Thepresently claimed invention addresses this felt need.

The preferred embodiment of the present invention employs a fieldasymmetric ion mobility filtering technique that uses high frequencyhigh voltage waveforms. The fields are applied perpendicular to iontransport, favoring a planar configuration. This planar configurationallows drift tubes to be fabricated inexpensively with small dimensions,preferably by micromachining. Also, electronics can be miniaturized, andtotal estimated power can be as low as 4 Watts (unheated) or lower, alevel that is suitable for field instrumentation.

Another advantage of the FAIMS device over the FIS device is the abilityto incorporate arrays of devices. The fact that arrays of FAIMS filtersis possible means that each filter in the array can be set to detect aparticular compound. Rather than having to change the filter conditionsto a different setting to detect a different compound, a number ofcompounds, defined by the number of filters in the array, can bedetected simultaneously.

It will now be appreciated that the present invention providesimprovements in methodology and apparatus for chromatographic high fieldasymmetric waveform ion mobility spectrometry, preferably including agas chromatographic analyzer section, intimately coupled with anionization section, an ion filter section, and an ion detection section,in which the sample compounds are at least somewhat separated prior toionization, and ion filtering proceeds in a planar chamber underinfluence of high field asymmetric periodic signals, with detectionintegrated into the flow path, for producing accurate, real-time,orthogonal data for identification of a broad range of chemicalcompounds.

The present invention provides improved chemical analysis bychromatography-high field asymmetric waveform ion mobility spectrometry.The present invention overcomes cost, size or performance limitations ofMS, TOF-IMS, FAIMS, and other prior art devices, in novel method andapparatus for chemical species discrimination based on ion mobility in acompact, fieldable package. As a result a novel planar, high fieldasymmetric ion mobility spectrometer device can be intimately coupledwith a GC separator to achieve a new class of chemical sensor, i.e., theGC-PFAIMS chemical sensor. A fieldable, integrated, GC-PFAIMS chemicalsensor can be provided that can rapidly produce accurate, real-time ornear real-time, in-situ, orthogonal data for identification of a widerange of chemical compounds. These sensors have the further ability torender simultaneous detection of a broad range of species, and have thecapability of simultaneous detection of both positive and negative ionsin a gas sample. Still further surprising is that this can be achievedin a cost-effective, compact, volume-manufacturable package that canoperate in the field with low power requirements and yet it is able togenerate orthogonal data that can fully identify various a detectedspecies.

Examples of applications for this invention include chemical sensors andexplosives sensors, and the like. Various modifications of the specificembodiments set forth above are also within the spirit and scope of theinvention. The examples disclosed herein are shown by way ofillustration and not by way of limitation. The scope of these and otherembodiments is limited only as set forth in the following claims.

What is claimed is:
 1. Apparatus for characterization of achromatographic eluent, comprising: an input part, an ion filter partfor filtering ions, an output part, and a flow path connecting saidparts, said parts being supported by a support structure, said ionfilter part including at least a pair of filter electrodes on saidsupport structure, said flow path axis extending between said input partand said output part through said ion filter part, said input part forreceiving a chromatographic eluent, said eluent including at least oneanalyte, said analyte being represented by a chromatographic peak thatis associated with a chromatographic residence time, said peak having apeak duration in said ion filter part, said input part for delivering aflow of ions to said flow path, said flow of ions including at least oneion species associated with said analyte, said flow of ions flowingalong said flow path to said ion filter part, said ion filter partfiltering said flow of ions, said support structure including anelectrode support in said ion filter part adjacent to said filterelectrodes for support of said filter electrodes in said ion filterpart, said filter electrodes being separated and forming an analyticalgap in said ion filter part, said filter electrodes providing acompensated asymmetric filter field within said analytical gap, saidflow path extending through said analytical gap, wherein surfaces ofsaid flow path in said ion filter part are cooperatively defined by saidelectrodes and said support structure, said ion filter part forproviding said compensated asymmetric field across said flow pathtransverse to said flow path for selection of said at least one ionspecies out of said flow of ions, said selection being at least in partbased on mobility characteristics of said selected at least one ionspecies in said compensated asymmetric field, and said ion filter partpassing said selected at least one ion species to said output partwithin said peak duration for characterizing said at least one ionspecies within said peak duration, said characterizing being based onsaid passing of said selected at least one ion species.
 2. Apparatus ofclaim 1 further comprising a chromatograph for supply of said eluent andwherein said characterization includes identification of said analytebased on said retention time associated with said peak in saidchromatograph.
 3. Apparatus of claim 2 wherein said output part includesa detector for detection and identification of said at least one ionspecies, wherein said detection data includes (a) intensity of said atleast one ion species detection, (b) said retention time, and (c)conditions of said compensated high asymmetric field.
 4. Apparatus ofclaim 3 wherein said flow of ions includes reactant ions, wherein saiddetection data is compared to known data to make said identification ofsaid at least one ion species.
 5. Apparatus of claim 3 furthercomprising a display coupled to said output part for display of at leasttwo dimensional data representative of said detected species. 6.Apparatus of claim 1 wherein said input part is disposed to present saidchromatographic eluent in gas phase to said flow path.
 7. Apparatus ofclaim 1 wherein said input part includes an ionization section forionization of said analyte and said output part includes a detector forgeneration of detection data associated with said analyte, furthercomprising a control part coupled to said filter part for scanning ofsaid field compensation, wherein said analyte is ionized in saidionization section and generates a representative flow of ions that isdelivered in said flow path to said filter part, wherein said fieldcompensation is scanned a plurality of times by said control part andwherein a plurality of mobility spectra are generated for said flow ofions, and wherein said plurality of scans has a total duration less thansaid peak duration, for characterizing chemical species in said eluent.8. Apparatus of claim 7 further comprising a device housing, saidcontrol part having contacts associated with said housing forapplication to said ion filter part of an asymmetric field drive signal.9. Apparatus of claim 1 wherein said input part includes a gaschromatograph and an ionization section associated with said flow path,said chromatograph delivering said eluent into said ionization section,said ionization section generating said at least one ion species. 10.Apparatus of claim 1 wherein said peak includes multiple peak aspectsand wherein scanning of said compensated field is performed in saidfilter part for generating differential mobility spectra for saidmultiple peak aspects, said scanning being performed within a period ofless than said peak duration, for characterizing chemical species insaid eluent.
 11. Apparatus of claim 10 further comprising a control partfor control of said compensated asymmetric field, said control partscanning said field compensation by scanning a DC bias applied to saidfield.
 12. Apparatus of claim 10 further comprising a control partcoupled to said filter part for applying an asymmetric RF signal to saidfilter part to generate said compensated asymmetric field, said controlpart scanning said compensation by scanning an aspect of the RE signal.13. Apparatus of claim 12 wherein said aspect is the duty cycle of theRE signal.
 14. Apparatus of claim 12 further comprising a drift gastube, wherein said capillary column is housed within said drift gastube, said capillary column having a column outlet delivering saidcarrier gas and said drift gas flow surrounding said carrier gas flow atsaid column outlet.
 15. Apparatus of claim 1, wherein said input sectionfurther includes an inlet in said flow path and a gas chromatographhaving a capillary column for delivering a gas sample into said inlet,said gas sample including a compound-containing carrier gas, furtherincluding a drift gas source, said drift gas source supplying said driftgas into said inlet to carry said compound-containing carrier gas alongsaid flow path to said output section.
 16. Apparatus of claim 1 whereinsaid ion filter part defines a pair of electrode plates across said flowpath, said compensated asymmetric field being developed between saidelectrode places.
 17. Apparatus of claim 16 wherein said ion filter partis non-cylindrical and said filter electrodes are non-cylindrical. 18.Apparatus of claim 17 further comprising insulated substrates, saidelectrode plates located on said substrates in said ion filter part forformation of said filter electrodes.
 19. Apparatus of claim 18 furthercomprising a housing, wherein said substrates are incorporated into saidhousing, wherein said ion filter part comprises a pair of spaced-apartelectrodes facing each other over said flow path and supported by saidsubstrates.
 20. Apparatus of claim 19 wherein said filter electrodeshaving inner faces facing each other across said flow path for formingsaid filter field, said facing electrodes having outer faces positionedon said substrates.
 21. Apparatus of claim 1 further comprising a pairof substrates, wherein said flow path is formed incorporating saidsubstrates, wherein said ion filter part comprises a pair ofspaced-apart electrodes facing each other over said flow path andassociated with said substrates.
 22. Apparatus of claim 21 wherein saidfield is formed between said electrodes, wherein said field isnon-focusing.
 23. Apparatus of claim 22 wherein said electrodes areplanar.
 24. Apparatus of claim 22 wherein said electrodes are parallel.25. Apparatus of claim 22 wherein said substrates form a device housing,said device housing supporting said input part, said flow path, and saidoutput part.
 26. Apparatus of claim 1 further comprising a detector insaid output part for said ion detection, said filter part passingpositive and negative ions to said detector, wherein said detectorincludes a pair of electrodes, said electrodes biased and cooperativelyenabled for simultaneous detection of said positive and negative ionspassed by said filter part.
 27. Apparatus of claim 1 further comprisinga control part for control of said compensated asymmetric field, whereinthe trajectory of said ion species passing through said field isregulated by said control part, wherein the output section furtherincludes a detector, said detector including a plurality of electrodesin sequence to form a segmented detector, said segments separated alongsaid flow path to detect said passed ions spatially according to theirtrajectories, and said control part controlling said detection. 28.Apparatus of claim 1 wherein said flow path is operable at or aroundatmospheric pressure in air.
 29. Apparatus of claim 1 wherein said ionfilter part includes an array of filters, each filter including a pairof electrodes in said flow path.
 30. Apparatus of claim 1 furtherincluding a heater in said flow path.
 31. Apparatus of claim 1 whereinsaid chromatograph is a gas chromatograph and said drift gas is air. 32.Apparatus of claim 1 further comprising an isolation part joining saidion filter part and said output part, said isolation part facilitatingnon-conductive connection of said ion filter part and said output part.33. Apparatus of claim 1 further comprising a plurality of electrodeswhich comprises array of electrodes formed in said flow path. 34.Apparatus of claim 33 further comprising a plurality of dedicated flowpaths communicating with said output section, wherein said plurality ofelectrodes comprises an array of filter electrode pairs associated withsaid dedicated flow paths.
 35. Apparatus of claim 1 further comprising apair of substrates, wherein said flow path is formed incorporating saidsubstrates, wherein said filter electrodes face each other over saidflow path and are associated with said substrates, further comprising atleast one pair of detector electrodes, one said detector electrodeassociated with each said substrate.
 36. Apparatus of claim 1 furthercomprising a plurality of electrodes forming a segmented detector withseveral segments, said segments being formed in a longitudinal sequencealong said flow path in said output part.
 37. Apparatus of claim 1further comprising a flow pump for drawing a fluid gas sample throughsaid flow path from said input part to said output part.
 38. Apparatusof claim 37 further comprising a plurality of dedicated flow paths,wherein said input part includes an ionization source for saidionization of gas samples drawn by said flow pump, further comprising asecond pump for recirculation of air in at least one of said flow paths.39. Apparatus of claim 1 wherein said compensated asymmetric field isdeveloped between said electrode plates, further comprising a pair ofinsulated substrates forming surfaces of said flow path, said electrodeplates formed on said substrates in said ion filter part.
 40. Apparatusof claim 39 further comprising a third substrate, wherein saidsubstrates define at least two adjacent flow paths.
 41. Apparatus ofclaim 39 further comprising a spacer extending along said flow axisbetween said input part and said output part and said filter electrodescooperating with said spacer to define said gap.
 42. Apparatus of claim41 wherein said spacer cooperates with said substrates and saidelectrodes to form a device housing enclosing said flow path. 43.Apparatus of claim 42 wherein said spacer is silicon and definesconfining electrodes in said flow path, further including a detectordownstream from said ion filter part for detecting ions traveling fromsaid filter part under control of said confining electrodes. 44.Apparatus of claim 1 further comprising a heater in said flow path forheating and purging said flow path.
 45. Apparatus of claim 44 furthercomprising insulated substrates, said ion filter part including filterelectrodes formed on said substrates, wherein filter electrodes can beused as heater electrodes.
 46. Apparatus of claim 1 further comprising acontrol part coupled to said filter part for scanning of said fieldcompensation in said filter part for generating differential mobilityspectra for representing analytes in said eluent said scanning beingperformed within a period as long as or less than said peak duration andgenerating multiple detection data for characterizing said analytes. 47.A method for analysis of compounds in a chromatographic eluent,including the steps of: providing a high field asymmetric ion mobilityfilter system with an internal flow path, enabling attachment of theoutput of a chromatograph system to said flow path, said flow pathopening into the input part of a said high field asymmetric ion mobilityfilter system, said system further including, an ion filter part forfiltering ions, and an output part, said flow path connecting saidparts, supporting said parts with a support structure, said ion filterpart including at least a pair of filter electrodes, said filterelectrodes being on said support structure, providing said supportstructure with an electrode support in said ion filter part adjacent tosaid filter electrodes for support of said filter electrodes in said ionfilter part, said filter electrodes being separated and forming ananalytical gap in said ion filter part, said flow path extending throughsaid analytical gap, defining said analytical gap as well as the sidesof said flow path in said ion filter part by cooperation of said supportstructure, said filter electrode support and said filter electrodes,providing a compensated asymmetric filter field within said analyticalgap between said electrodes, separating at least one analytechromatographically from a chemical mixture and eluting said separatedanalyte into said flow path, said analyte forming a chromatographic peakthat is associated with a chromatographic residence time, said peakhaving a peak duration of some time period, providing a flow of ions tosaid ion filter part in said flow path within said time period,including the step of ionizing at least a portion of said separated atleast one analyte and forming at least one ion species, furtherincluding flowing said at least one ion species into said flow of ionswithin said time period, providing said compensated asymmetric filterfield transverse to said flow path in said ion filter part within saidtime period, filtering said flow of ions within said time period andselecting said at least one ion species out of said flow of ions, saidselection being made according to aspects of ion mobilitycharacteristics of said at least one ion species in said transversefield within said time period, and passing said selected at least oneion species to said output part within said time period forcharacterization of said at least one analyte according to mobilitycharacteristics of said selected at least one ion species in saidtransverse field within said time period.
 48. Method of claim 47 whereinsaid system further includes a housing for containing said ion filterand said internal flow path, further including the step of providingsaid filter with filter electrodes having inner faces facing each otheracross said flow path for forming said field, said facing electrodeshaving outer faces associated with said housing.
 49. Method of claim 47wherein said time period is about a second or less.
 50. Method of claim47 further comprising said the step of applying a drift gas to saideluted analyte to increase said flow volume and velocity of said ionsthrough said system.
 51. Method of claim 50 wherein said analyte iseluted from a capillary column of a gas chromatograph, furthercomprising said step of surrounding said capillary column outlet withsaid flowing drift gas.
 52. Method of claim 51 further including thestep of forming reactant ions in said flow of ions, said reactant ionsreacting with said ionized sample to create reactant ion data peaks,further comprising said step of obtaining chromatographic retention timerelated to said analyte by monitoring fluctuation in intensity of saidreactant ion data peaks.
 53. Method of claim 52 further comprising stepsof applying a high asymmetric RF field in said filter and detectingpositive and negative ions simultaneously passing through said high REfield for identification of at least one ion species passed by saidfilter.
 54. Method of claim 47 further comprising the step of collectingdetection data and obtaining retention time, compensation voltage anddetection intensity, and relating this data to a store of data toidentify said detected species.
 55. Apparatus for fast characterizationof a chromatographic sample, comprising: an input part, an ion filterpart for filtering ions in an electric filter field, an output part, anda flow path connecting said parts, said parts being supported by asupport structure defined by cooperating substrates, said ion filterpart including at least a pair of plate-type filter electrodes on saidsubstrates in said ion filter part and forming conductive electrodesurfaces, said substrates forming other supporting surfaces in said ionfilter part that support said electrodes in said ion filter part, saidelectrodes separated from each other and defining an analytical gap insaid ion filter part, said filter field being generated across said flowpath in said gap, said filter electrodes providing a compensatedasymmetric RF filter field within said gap, wherein surfaces of said gapin said ion filter part are cooperatively defined by said electrodes andsaid support structure, said input part for receiving a chromatographiceluent, said eluent including at least one analyte, said input part fordelivering a flow of ions to said flow path, said flow of ions includingat least one ion species associated with said analyte, said ion filterpart filtering said flow of ions in said compensated asymmetric RFfilter field in said gap, wherein said analyte is represented by achromatographic peak flowing at a selected flow rate, said peak having apeak duration in said ion filter part, and wherein said ion filter partpasses said selected at least one ion species to said output part withinsaid peak duration for characterizing said at least one ion specieswithin said peak duration according to aspects of ion mobility in thefilter field.
 56. Apparatus of claim 55 wherein said filter electrodesare formed as plates on said substrates, said substrates isolating saidplates from each other, wherein said RF field is generated between saidplates in said gap.
 57. Apparatus of claim 56 wherein said flow path haswalls in said ion filter part, wherein said plates extend along aportion of said walls and wherein said substrates extend along anotherportion of said walls in said ion filter part.